Like Dissolves Like
The empirical rule that substances dissolve best in solvents with similar polarity and bonding character.
Unit
Dimensionless
In depth
A solute dissolves readily when the solute–solvent interactions it can form are comparable in strength to the interactions being broken. Polar and ionic solutes therefore prefer polar solvents, while non-polar solutes prefer non-polar ones. Molecules with both characters, such as short alcohols, dissolve in both.
Examples in the real world
Salt and sugar dissolve in water; wax and iodine dissolve in hexane; ethanol dissolves in both.